btrfs: Refactor main loop in extent_readpages (61ed3a14) · Commits · 戴 / test

extent_readpages processes all pages in the readlist in batches of 16, this is implemented by a single for loop but thanks to an if condition the loop does 2 things based on whether we've filled the batch or not. Additionally due to the structure of the code there is an additional check which deals with partial batches. Streamline all of this by explicitly using two loops. The outter one is used to process all pages while the inner one just fills in the batch of 16 (currently). Due to this new structure the code guarantees that all pages are processed in the loop hence the code to deal with any leftovers is eliminated. This also enable the compiler to inline __extent_readpages: ./scripts/bloat-o-meter fs/btrfs/extent_io.o extent_io.for add/remove: 0/1 grow/shrink: 1/0 up/down: 660/-820 (-160) Function old new delta extent_readpages 476 1136 +660 __extent_readpages 820 - -820 Total: Before=44315, After=44155, chg -0.36% Signed-off-by:

Nikolay Borisov <nborisov@suse.com> Reviewed-by:

David Sterba <dsterba@suse.com> Signed-off-by:

David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

+14 −20

Original line number	Diff line number	Diff line
		@@ -4094,42 +4094,36 @@ int extent_readpages(struct address_space mapping, struct list_head pages,
		unsigned nr_pages)
		{
		struct bio *bio = NULL;
		unsigned page_idx;
		unsigned long bio_flags = 0;
		struct page *pagepool[16];
		struct page *page;
		struct extent_map *em_cached = NULL;
		struct extent_io_tree *tree = &BTRFS_I(mapping->host)->io_tree;
		int nr = 0;
		u64 prev_em_start = (u64)-1;

		for (page_idx = 0; page_idx < nr_pages; page_idx++) {
		page = list_entry(pages->prev, struct page, lru);
		while (!list_empty(pages)) {
		for (nr = 0; nr < ARRAY_SIZE(pagepool) && !list_empty(pages);) {
		struct page *page = list_entry(pages->prev,
		struct page, lru);

		prefetchw(&page->flags);
		list_del(&page->lru);
		if (add_to_page_cache_lru(page, mapping,
		page->index,
		if (add_to_page_cache_lru(page, mapping, page->index,
		readahead_gfp_mask(mapping))) {
		put_page(page);
		continue;
		}

		pagepool[nr++] = page;
		if (nr < ARRAY_SIZE(pagepool))
		continue;
		__extent_readpages(tree, pagepool, nr, &em_cached, &bio,
		&bio_flags, &prev_em_start);
		nr = 0;
		}
		if (nr)

		__extent_readpages(tree, pagepool, nr, &em_cached, &bio,
		&bio_flags, &prev_em_start);
		}

		if (em_cached)
		free_extent_map(em_cached);

		BUG_ON(!list_empty(pages));
		if (bio)
		return submit_one_bio(bio, 0, bio_flags);
		return 0;

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